1. Field of the Invention
The present invention is related to a method and device for driving a light-emitting diode, and more particularly, to a method and device for driving the light-emitting diode by an alternating current voltage.
2. Description of the Prior Art
A light-emitting diode (LED) is characterized by low power consumption, long lifetime and short reaction time, and therefore LED lamps are gradually replacing traditional tungsten lamps and fluorescent lamps. Similar to the tungsten lamp, light emitted by the LED lamp is adjusted based on practical requirements. Since the LED benefits from short reaction time, the LED lamp is generally controlled according to a pulse width modulation (PWM) scheme. That is, the LED lamp controls brightness by adjusting a “lit” duty cycle of the LED.
In general, to employ the PWM scheme, the LED lamp first has to convert an alternating current (AC) voltage, such as a voltage provided by mains power, into a direct current (DC) voltage, so as to process following logic operations. To convert the AC voltage into the DC voltage, the LED lamp has to include a large capacitor as a charge exchanging medium. However, partial LED lamps are not allowed to include the large capacitor due to cost and specification concerns. Therefore, if the LED is directly driven by the AC voltage, manufacturing costs and design complexity of the LED lamp can be effectively reduced.
Therefore, directly driving the LED by the AC voltage has been a major focus of the industry.